Method and apparatus for rolling metal strip and sheet



April 2, 1968 u. H. TAYLOR 3,375,588.

METHOD AND APPARATUS FOR ROLLING METAL STRIP AND SHEET Filed May 19,1965 14 Sheets-5heet l INVENTOR. Louis H. Taylor BY W LL 6W,

H/S ATTORNEYS April 1968 L. H. TAYLOR 3,375,688

METHOD AND APPARATUS FOR ROLLING METAL STRIP AI ID SHEET Filed May 19,1965 14 Sheets-Sheet 2 0 0 u I ----0 -0 AMPLIFIER AMPLIFIER Fig.5 IFig.6

INVENTOR. I Louis H. Taylor BY 6%,

H/S ATTORNEYS April 2, 1968 L. H. TAYLOR 3,375,583

METHOD AND APPARATUS FOR ROLLING METAL STRIP AND SHEET Filed May 19,1965 14 Sheets--Sheet 5 TRANSDUCER LV DT INVENTOR. Louis H. Taylor BYWM, 6

QMQ'WM HIS A TTORNE Y5 L. H. TAYLOR April 2, 1968 METHOD AND APPARATUSFOR ROLLING METAL STRIP AND SHEET 14 Sheets--Sheet 5 Filed May 19, 1965iq. IO

/N l E N T 05. Louis H. Taylor HIS ATTORNEYS H. TA YLOR 3,375,688

METHOD AND APPARATUS FOR ROLLING METAL STRIP AND SHEET A ril 2, 1968 14Sheets-$heet 6 Filed May 19, '1965 April 1968 H. TAYLOR 3,375,688

METHOD AND APPARATUS FOR ROI JLING METAL STRIP AND SHEET Filed May 19,1965 14 Sheets-Sheet 7 I38 I39 I40 I32 5:; I37 A 93 A {Isl I05 I07 87 AL l 4 l? Fig.1.? W M W INVENTOR.

Louis H. Taylor w 5M, WI/w I f i HIS ATTORNEYS April 2, 1968 1.. H.TAYLOR 3,375,688

METHOD AND APPARATUS FOR ROLLING METAL STRIP AN D SHEET 7 Filed May 19,1965 14 Sheets-$heet 8 INVENTOR. Louis H. Taylor Fig.1.? Byw {Us I JM+HIS A TTOfi/VEYS p 968 L.VH.TAYLOR 3,375,688

METHOD AND APPARATUS FOR ROLLING METAL STRIP AND SHEET Filed May 19,1965 14 heets-Sheet a Louis H. Taylor JAGM. I? 7" W116 H/S A TTORNEYS L.H. TAYLOR April 2, 1968 METHOD AND APPARATUS FOR ROLLING METAL STRIP ANDSHEET Filed May 19, 1965 14 Sheets-$heet 10 Taylor INVENTOR. Louis H. BYI KM MM- HIS. ATTORNE rs April 2, 1968 HfTAYLOR 3,375,688

METHOD AND APPARATUS FOR ROLLING METAL STRIP AND SHEET Filed May 19 19 5l 14 Sheets-Sheet 12 mam/r A c 6% INPUT ,4-

2 F; C D 233 t zaq F2 z 4 m 229 ROLL 2- P'REE FflA 52/005 mew/m5 225 225LOU/S H M 25 4( 0A 06 v a) #v ur u (5 .1...

ERROR 11L SIG/VAL i WM" w L. H. TAYLOR April 2, 1968 METHOD ANDAPPARATUS FOR ROLLING METAL STRIP AND SHEET l4 Sheets-Sheet 1'5 FiledMay 19, 1965 mw M INVENTOR.

LOU/5 H. 721M! 0 BY PM W April 2, 1968 L. H. TAYLOR METHOD AND APPARATUSFOR ROLLING METAL STRIP AND SHEET l4 Sheets-Sheet 14.

Filed May 19, 1965 UPPER ROL L OlQ/I/E' REACT/0N Tf/QUSTJ/DE IN VEN TORLOU/5 h. 7I4YLOJQ BY LL aw. {M M HA5 ATTOR/VEVS United States Patent3,375,688 METHOD AND APPARATUS FOR ROLLING METAL STRIP AND SHEET LouisH. Taylor, Youngstown, Ohio, assignor to The Youngstown Research andDevelopment Company, Youngstown, Ohio, a corporation of OhioContinuation-impart of application Ser. No. 239,199, Nov. 21, 1962. Thisapplication May 19, 1965, Ser. No. 457,104

27 Claims. (Cl. 7221) ABSTRACT OF THE DISCLOSURE A method and apparatusfor rolling metal sheet in a rolling mill a small diameter work roll andat least one upper and one lower backing roll for the work roll whichare driven by separate motors in which deflection of the small work rollis controlled by effecting changes in apportionment of the torqueapplied by the motors to the driven backing rolls. Means are provided tosense the amount and direction of the deflection of the small Work rollwhich produces a signal related to the amount and direction of thedeflection. An error signal is produced related to the differencebetween the sensed position and the desired position and transmitted tothe motors to effect changes in apportionment of the applied torque andthereby control deflection of the work roll and the shape of the issuingstrip.

This application is a continuation-in-part of my application Ser. No.361,418, filed Apr. 21, 1964, now Patent No. 3,275,918, which is acontinuation-in-part of my application Ser. No. 239,199, filed Nov. 21,1962, now abandoned, which is a continuation-in-part of my applicationSer. No. 734,321, filed May 9, 1958, now Patent No. 3,077,800.

This invention relates to a method and apparatus for rolling metal stripand sheet, and more particularly to a method and apparatus formaintaining deflection of a small diameter work roll of a roll standsubstantially at a given position in the roll pass of the stand. Thedeflection to which my invention relates is in a direction with andopposite to travel of metal through the mill, and the small work roll isone of a plurality of rolls of a stand, all of whose longitudinal axesare in substantially the same vertical plane.

Generally, this small diameter work roll is on a -high stand, a 3-highstand, a 4-high stand, or a 6-high stand where it is the smallestdiameter roll of the stand. On the S-high stand, it has an upper andlower intermediate roll each of larger diameter and an upper and a lowerbacking roll each of greater diameter than the intermediate rolls andeach backing roll in frictional engagement with its intermediate roll.This work roll is in frictional engagement with the one intermediateroll and forms with the other intermediate roll a roll pass throughwhich the metal travels and in which it is reduced in thickness.

On the 3-high mill, the roll is the smallest roll and is disposedbetween two backing rolls, each of which is driven by an electric motor.

On the 6-high mill, this small diameter work roll forms with a largerdiameter work roll the roll pass. The diameter of the larger work rollis substantially about one and onehalf to four times the diameter of thesmall work roll. The two work rolls are interposed between upper andlower intermediate rolls which, in turn, are interposed between upperand lower backing rolls. The upper intermediate roll is in frictionalengagement with one of the work rolls and the lower intermediate roll isin frictional engagement with the other work roll while the upperbacking and upper intermeditae rolls are in frictional engagement as arethe lower intermediate and lower backing rolls.

The given position of the small work roll in the roll pass can be one atwhich the longitudinal axis of the small work roll is in verticalalignment with the longitudinal axes of the other rolls of the mill orit can be one at which the small work roll is bowed or deflected in adirection with or opposite to travel of metal through the mill. In thislatter case, the longitudinal axis of the small work roll is not invertical alignment with the longitudinal axes of the other rolls of themill. Selection of the given position is dependent upon production of adesired shape in the rolled metal which in most cases is flat, and takesinto consideration crown in the rolls due to the shape of the rollbodies and/ or to heat generated by reduction of the metal. During thecourse of rolling, the given position may be changed intentionally toobtain a desired shape in the metal or to maintain shape. This change inthe given position may be required because of variations in conditionsin the roll pass such as heat build-up in the roll body or bodies orbecause of variations in the metal itself, such as hard spots oroff-gauge.

Driving force or torque for the small work results from frictionalengagement with at least one backing roll or intermediate roll and fromapplication of forward tension to the metal by a winding reel or anotherstand on the exit side thereof.

In recent years, there has developed an increasing demand for wide metalstrip and sheet, particularly in the very thin gauges such as 0.001 to0.008" with a special emphasis upon flatness. Although it is recognizedthat small diameter work rolls readily bite into the metal being rolled,reduce screw pressures and make reductions in gauge of the metal whichcannot be made with larger diameter rolls, efforts to use such smalldiameter rolls, especially those which are too small to be driventhrough their necks (those with diameters 1" to 4") have beenunsuccessful. This has resulted from inability to control the deflectionof these rolls in the plane of metal travel through the mill as aconsequence of which it has been highly difficult to obtain a specifieddegree of flatness in the strip or sheet. The uncontrolled deflection orbowing of the small diameter work roll causes over-rolled edges orripples and/or over-rolled center portions or buckles in the strip. Whenthis occurs in the thin gauges, it is costly and troublesome, if notimpossible, to remove the buckles and riflles and off-gauge strip isproduced, thereby rendering it unsatisfactory for specifications andorders.

Two factors can cause this deflection, the first being an unbalance offorce acting upon the small work roll and the second being a combinationof forces generated by the screwdown mechanism of the stand acting uponthe top backing roll and of the tolerances in the bearings and chocksfor the backing rolls, intermediate: rolls and the work roll.Considering first the deflection caused by the unbalance of forcesacting upon the rolls, and referring to FIGURE 1 which showsdiagrammatically a S-high mill, that mill comprises a top backing roll 1and a bottom backing roll 2 with a top intermediate roll 3 and a lowerintermediate roll 4 disposed therebetween. The top intermediate roll isin frictional engagement with the top backing roll, and the lowerintermediate roll is in frictional engagement with the bottom backingroll with the backing rolls being driven by electric motors, not shown.However, the intermediate rolls can be driven instead of the backingrolls. Disposed between the two intermediate rolls is a small diameterwork roll 5 in frictional engagement with the lower intermediate roll 4and forming a roll pass with the top intermediate roll 3. Extendingthrough the roll pass is metal strip 6.

A combination of two resulting forces rotates the work roll 5. The firstresulting force acts on the top side of the roll and comprises a portionof strip delivery tension T and tangential force F generated by the topbacking roll 1 acting upon the top intermediate roll 3 and extendingtransversely through the strip thickness to the top part of the workroll 5. The sum of these two forces tends to move the roll 5 towards thedelivery side of the mill as shown by arrow 7.

The second resulting force acts on the lower side of the work roll 5 andcomprises a tangential force F produced by rotation of the lower backingroll 2 in frictional engagement with the intermediate roll 4. The othercomponent of this second resulting force is the entry tension T which,together with the tangential force F acts to move the work roll 5towards the entry side of the mill as shown by arrow 8. Consequently,for equilibrium conditions corresponding to a servo lateral deflectionand zero bearing loads on the rolls, the following condition exists: (T+F )=(T +F The second factor which causes the deflection results from acombination of forces generated by operation of a screwdown mechanismand of tolerances in the roll bearings and chocks. When the screwdownmechanism lowers the top backing roll and the top intermediate roll toestablish a given roll pass to effect a particular reduction, thescrewdown mechanism exerts a force On the rolls. This force, incombination with the tolerances between the roll necks, the bearingsand/ or the chocks and tolerances in the mill housing, may cause thework roll to deflect in the direction with or opposite to travel ofstrip through the mill. Such deflection occurs because of the smallamount of space between the bearings and the roll neck and between thechocks and the mill housings, thus enabling the roll necks and/or shocksto shift or move a small amount when subjected to the screwdown force.

Control over deflection of the small work roll to obtain a desired shapeor flatness in the strip encounters further complications from a heatbuild-up in the rolls, especially during sustained rolling periods. Thisheat build-up cannot be completely dissipated by flood coolant andgenerally effects an expansion or swelling commonly called crown in acenter portion of the small roll and/or in any other roll. Presence ofthe crown causes over-rolling of the center portion of the strip,thereby requiring compensation in the position of the small roll in theroll pass to minimize if not eliminate its effect upon the shape of thestrip. Thus, regulation of deflection of the single small roll presentsmany problems which place severe requirements upon a control systemtherefor.

Full realization of advantages from use of the single small diameterwork roll has been hampered by inability to very quickly effect acorrection or compensation for deflection to maintain or return the rollat or to a given position in the roll pass. Since the metal is travelingthrough the mill at speeds from about 500 f.p.m. to about 6,000 f.p.m.,a substantial amount of defectively-shaped strip can result where even a24 second period is c0nsumed in returning the work roll to its givenposition. Production of defectively-shaped strip is unwanted for it musteither be cut out of the coil or the coil diverted to another order,thereby materially increasing costs of manufacture.

My invention permits full utilization of the advantages of the smalldiameter work roll by maintenance of de flection of the roll at a givenposition in the roll pass and by ability to effect an extremely fastcorrection for deviations in deflection from the given position.Specifically, it comprises maintaining the deflection of a smalldiameter work roll substantially at a given position in the roll passand/or controlling the amount of deflection of this work roll in theroll pass on a rolling mill which has at least one upper backing and atleast one lower backing roll for the work roll. This deflection of thesmall work roll is in the direction substantially with and substantiallyopposite to travel of the metal through the mill. Each of the backingrolls has a diameter greater than the diameter of the small work rolland the rolls are disposed substantially vertically of one another. Thework roll and one of the upper and lower backing rolls form a roll passthrough which metal is reduced in thickness and another backing roll isin frictional engagement with the work roll. At least one electric motoris operatively connected to an upper backing roll and at least oneelectric motor is operatively connected to a lower backing roll.Maintenance and/or control of the deflection results from increasing anddecreasing the amount of the deflection by effecting changes inapportionment of applied torque by the motors between the driven rollsthrough sensing amount and direction of deflection of the work roll fromthe given position. From this sensing, a signal related to the amount ofdeflection and related to the direction thereof is generated and thenfrom the signal an error signal related to the difference between thesensed position of the work roll and the given position of the work rolland related to the direction of deflection is produced. Thereafter, theerror signal is utilized in regulation of output torque of the electricmotors for effecting the changes in apportionment of applied torque tothe driven rolls to maintain the small work roll substantially at thegiven position. Preferably, the sensing of deflection of the small workroll includes sensing the rate of change of deflection and the signal isrelated to the rate of change of deflection. Further, the error signalis related to the rate of change of difference between the sensedposition and the given position of the small work roll.

In one embodiment of my invention, a current related to the magnitude ofthe error signal and related to the direction of the error signal isproduced from this error signal and then applied to the electric motorsfor effecting the changes in apportionment of applied torque to thedriven rolls to maintain the small work roll substantially at the givenposition or to control the amount of deflection of the small work roll.The current which is produced from the error signal is appliedpreferably to the armatures of the electric motors to effect the changesin apportionment of applied torque, but it can alternatively be appliedto the fields of the electric motors to effect the changes inapportionment. One such current which I have employed comprises a firstpart which is substantially continuous, is related in magnitude to theamount of the deflection and related to the direction of the deflection.This current also has a second part which is pulses of short durationrelated in magnitude to the amount of the deflection and related to thedirection of deflection. The first part is a major portion of thecurrent and requires a longer time interval to effect a change inapportionment of applied torque than the second part.

I prefer to effect these changes in apportionment of applied torquewithout substantially affecting the amount of total torque delivered tothe driven rolls. Such is accomplished by increasing amount of appliedtorque to one of the driven rolls by increasing output torque of themotor or motors connected thereto, while simultaneously decreasing theamount of applied torque delivered to the other driven roll bydecreasing output torque of its motor or motors. In this way, the smallwork roll is brought back from its deflected position towards the givenposition. In practice of my method, I can so carry out the sensing ofdeflection and utilization of the error signal that deflection of thesmall work roll is maintained within a range of substantially $00005" ofthe given position. A range of deflection of :0.005" and more can beused for some rollings. This range of deflection in which the small workroll is maintained is in part dependent upon the flatness of the strip,the width of the mill and the diameter of the small roll.

My invention also includes a method of rolling the strip in which a milloperator observes the shape of the strip as it issues from the mill andthen, based upon his observation, he controls the amount of deflectionof the small work roll to produce a desired shape. In controlling theamount of deflection he increases and/or decreases the amount ofdeflection of the small work roll through making changes inapportionment of the torque applied by the motors to the driven upperand lower rolls. Such changes in apportionment of the torque compriseincreas ing or decreasing the amount of output torque of the motor ormotors which rotate one driven roll relative to the amount of outputtorque of the motor or motors which turn the other driven roll throughoperation of controls for the motors.

While entry and delivery tension upon the metal strip have an affectupon deflection of the small work roll, I effect maintenance ofdeflection of this small work roll at the given position in the rollpass through control over the torque applied to the driven rolls of themill and not through regulation of amounts of tension in the strip. Fromthe standpoint of mill operation, it is preferable to independentlyregulate amounts of tension in the strip and not attempt to controldeflection of the small work roll by changing amounts of tension appliedto the metal strip. This is particularly true in rolling the very thinstrip, some of which has low yield strengths, wherein it is important toclosely maintain amounts of tension within allowable unit stress andthereby avoid strip breakage.

My invention in apparatus for maintaining deflection of the smalldiameter work roll substantially at a given position in the roll passcomprises a means for sensing amount and direction of the deflectionwith this sensing means disposed opposite a face of the roll so thatdeflection is toward and away therefrom. Connected to the sensing meansis a signal generating means which produces from the deflection a signalrelated to the amount of deflection and related to direction of thedeflection. Connected to the signal generating means is an error signalgenerating means which produces from the signal an error signal relatedto the difference between a sensed position of the small work roll andthe given position of this small work roll, and is related to thedirection of the deflection. An error signal transmitting means isjoined to the error signal generating means and connected to one of theelectric motors which are drivingly connected to rolls of the mill andof means coupled to the electric motors for regulating output torque ofthese motors to effect changes in apportionment of applied torque to thedriven rolls to maintain the small work roll substantially at the givenposition.

Preferably, the signal generating means is such that the signal is alsorelated to rate of change of deflection of the small work roll and theerror signal generating means is such that the error signal is alsorelated to rate of change of deflection of this small work roll.

In one embodiment of the apparatus, the error signal generating means isconnected to a current producing means and utilizes the error signal togenerate a current related to the magnitude of the error signal andrelated to its direction. This current is then transmitted to theelectric motors for regulating their operation to control output torqueand thereby effect the changes in apportionment of applied torque to thedriven rolls. This current is applied, preferably, to the armatures ofthe electric motors, but can also be applied to the fields of theseelectric motors.

The means coupled to the electric motors for regulating their outputtorque includes a controllable variable load producing device whichregulates output torque of the electric motors, in connected to theerror signal generating means, and is responsive to the error signal foreffecting the changes in apportionment of applied torque. Examples ofthe controllable variable load producing device include electricallyoperated friction brakes which are disposed in engagement with theoutput shaft of the electric motors and which include an eddy currentabsorption dynamometer with a DC. excitation winding regulated by theerror signal or a current produced therefrom in push-pull manner with noresultant mill speed change or with a non-overlapping individualloadcontrol; gener ators which are coupled to the motors, whose output isdissipated as heat through load resistors: and whose field is regulatedthe same as the above dynamometer; generators which are coupled to theelectric motors from which power is recovered, and whose fields arecontrolled the same as the above dynamometer; and hydraulic load deviceswhich work upon the output shafts of the electric motors. All of thesedevices are responsive to the error signal for effecting the changes inapportionment of the applied torque.

The small work rolls to which my invention is especially directed mayhave diameters ranging from about A" to about 8.

In the accompanying drawings, I have shown preferred embodiments of myinvention, in which:

FIGURE 1 shows diagrammatically a 5-high mill;

FIGURE 2 is a schematic view of one device for detecting deflection ofthe single small roll of a S-high mill;

FIGURE 3 is a schematic view of a second sensing device;

FIGURE 4 is a schematic view of a third sensing device;

FIGURE 5 is a schematic view of a fourth sensing devlce;

FIGURE 6 is a schematic view of a fifth sensing device;

FIGURE 7 is a schematic view of a sixth sensing device;

FIGURE 8 is a schematic diagram showing my invention applied to aZ-stand, S-high tandem mill;

FIGURE 9 is a block-diagram of apparatus for generating the error signalwhich is used to maintain deflection of the roll at a given position;

FIGURE 10 is a schematic wiring diagram of one embodiment of a slowacting regulating system and a fast acting regulating system whichreceives the error signal and generates therefrom a reversible push-pullcontinuous current and reversible push-pull pulses of current forproducing the regulated buck-boost output armature current;

FIGURE 11 is a schematic wiring diagram showing a first modification ofthe embodiment of FIGURE 10;

FIGURE 12 is a schematic wiring diagram of a second modification of theembodiment of 'FIGURE 10;

FIGURE 13 is a schematic wiring diagram of a second fast regulatingsystem for the embodiment of FIGURE 10;

FIGURE 14 is a schematic wiring diagram of a third fast regulatingsystem for the embodiment of FIGURE 10:

FIGURE 15 is a schematic wiring diagram of a third modification of theembodiment of FIGURE 10;

'FIGtURE 16 is a schematic wiring diagram of a fourth modification ofthe embodiment of FIGURE 10;

FIGURE 17 is a schematic wiring diagram of a system which receives theerror signal and generates therefrom a current which is delivered to thearmatures of the electric motors which are drivingly connected to rollsof the mill for effecting changes in apportionment of applied torque tothe driven rolls;

FIGURE 18 is a block diagram similar to that of FIG- URE 9, but adaptedto the system of FIGURE 17;

FIGURE 19 is a schematic wiring diagram of a system which receives theerror signal and generates therefrom a current which is delivered to thefields of the electric motors which are drivingly connected to rolls ofthe mill;

FIGURE 20 is a schematic diagram of a G-high mill equipped with myinvention; and

FIGURE 21 is a schematic diagram of a drive for a rolling mill withchanges in apportionment of applied torque to the driven rolls of themill effected through electrically operated friction brakes connected todriven spindles which are joined to the driven rolls.

Referring to FIGURES 2, 9 and 10, the S-high mill of FIGURE 1 mountsapparatus 9 for detecting deflection of the single small diameter 'WOIkroll in a roll pass formed by the upper intermediate roll 3 and thesmall diameter roll itself. As shown, the lower backing roll 2 is drivenby two motors 10 and 11 connected in tandem with motor 10 being shown inFIGURE 2, and the top backing roll is driven by two motors 12 and 13connected in tandem. The upper intermediate roll 3 is in frictionalengagement with the upper backing roll 1 and the lower intermediate roll4 is in frictional engagement with the lower backing roll 2. Although Ihave shown the roll drive connected to the backing rolls, it mayalternatively be joined to the intermediate rolls, one of which alsofunctions as a backing roll for the work roll 5.

Connected to the sensing apparatus 9 is a signal gen-' erator 14 whichproduces from deflection of the roll 5 a signal related in magnitude andrelated to direction of the deflection. This signal travels to apush-pull output amplifier 15 (FIGURE 9) where a first portion continuesto a push-pull driver amplifier 16 whose output is delivered to a slowacting regulating system 17 (FIGURE 10) and a second portion advances toa bias and trigger generator combination 19 whose output is transmittedto a fast action regulating system 19. The slow regulating systemproduces a reversible push-pull substantially continuous current and thefast regulating system generates reversible push-pull pulses of currentof short duration. These two currents are fed to a buck-boost generator20 whose output is applied to the armatures of the motors for drivingthe backing rolls 1 and 2. By boosting the armature current of one rolldrive motor combination and bucking the armature current of the otherroll drive motor combination, 1 effect a change in apportionment oftorque applied to the driven rolls 1 and 2 to maintain the roll 5 at orreturn it to a given position in the roll pass.

Considering the sensing apparatus of FIGURE 2, nozzles 21 and 21aconnected to conduits 22 and 22a leading from a source of fluid underpressure such as air or liquid straddle both sides of the roll 5, aresubstantially opposite the face 24 of the roll 5, and are substantiallyin alignment with the center line of the roll and substantially midwaybetween the ends of the face 24 thereof so that deflection of the roll 5in the direction with or opposite to strip travel through the roll passis toward one nozzle and simultaneously away from the other nozzle.Safety bars 25 and 25a mount and position the nozzles opposite the rollface.

These nozzles are located close to the roll face across gaps 26 and 26abetween the ends of the nozzles and the roll face so that deflection ofthe roll '5 produces a change in pressure of the fluid under pressure inthe conduits. Preferably, the length of the gaps between the nozzle andthe roll face is from about 0.005 to about 0.050" when the roll and itsintermediate and backing rolls are in axial alignment as shown in FIGURE1.

Within the range of deflection of the roll 5, impingement of two jets ofair or fluid against the roll face produces back pressure in theconduits 22 and 22a with this back pressure being less when the roll isdeflected away from one nozzle to lengthen the gap and greater when thedeflection is toward the nozzle to shorten the gap. When the rolls 5, 1,2, 3 and 4 are in axial alignment, impingement of the two jets againstthe roll face produces equal amounts of back pressure in the conduits 22and 22a. The back pressure affects the pressure of air or fluid formingthe jet and as the gap shortens, the back pressure increases and as thegap lengthens, it decreases. Accordingly, as the work roll 5 deflectstoward the nozzle 26, back pressure in the conduit 22 increases, therebyreducing the strength of the jet from the nozzle 26 and increasingpressure in the conduit 22. Simultaneously, the roll 5 deflects awayfrom the nozzle 26a and decreases back pressure in conduit 22aaccompanied by an increase in pressure of the jet from the nozzle 26::and a decrease in pressure in the conduit 22a. This change in strengthsof the jets and the changes in pressures in the conduits are used fordetection of roll deflection and the magnitude of the changes arerelated to the amount of deflection and the direction of changedependent upon an increase or decrease in pressure.

To convert changes in fluid pressure in the conduits into a signal forcontrolling operation of the mill, the conduits are connected to asignal generator 14 comprising a transducer 27 and a linear variabledifferential transformer (LVDT) 28 whose output is transmitted to anamplifier 29. The operation of this transducer 27 and the linearvariable differential transformer is described in my Patent No.3,077,800.

FIGURES 3 and 4 show two other types of roll deflection sensing deviceswhich utilize electromagnetic induction to induce eddy currents in thesurface of the roll 5 where high frequencies such as 50 kilocycles andhigher are used, or to effect changes in the inductive reactance in oneor two electromagnetic inductors which changes correspond to shorteningand lengthening of gaps between the inductors and the roll face. Asshown in FIGURE 3, I locate two electromagnetic inductors 45 and 46, oneon each side of the small roll 5 and connect each inductor into a bridgecircuit 46a in which each inductor forms one arm of the reactancebridge. The other two arms of the bridge are resistors 45a and 45b ofselected values. The two corners of the bridge formed by the junctionsof the two resistors and the two inductors are connected to a highfrequency source 47a of alternating current as provided by the driveroscillator 75. The other two corners of the bridge formed by thejunctions of resistor 45a and inductor 45 and of resistor 45b andinductor 46 are the outputs of the reactance bridge and are connected tothe amplifier 29. The reactance bridge circuit has a null balance RCnetwork comprising a variable capacitor 450 and a variable resistor 45dconnected in parallel and across one input corner 45e and one outputcorner 45].

As to each inductor, changes in reactance as a result of roll deflectionare nonlinear. However, the two in combination, when disposed in thereactance bridge circuitry, will produce a substantially linear outputas a function of roll deflection.

Each inductor is spaced apart from the roll 5 to provide small gaps 48and 49 between the roll face and the leading face of each inductor, andeach inductor generates magnetic lines of flux which travel from theinductor across the gaps to the roll face. It has been found that a gapbetween the roll face and the leading face of the inductor of about0.005 to about 0.025" effects satisfactory detection of roll deflection.

For practical purposes, it is better to move the roll against oneinductor and null-balance the bridge. The output voltage of the bridgewill then be a function of the roll displacement away from that coil andwill rise to a maximum value when the roll is against the opposite coil.At a midway gap point, the output voltage will then be substantiallyone-half of its maximum value which is conducive to good detection andregulating techniques as it can now be matched against an equalreference voltage. Any deviation from this reference is detected by adifference amplifier 78 (FIGURE 9) which can now be further fed into theproper functional circuitry of a regulating system to restore balance.

The single inductor 51a of FIGURE 4 operates similarly to those ofFIGURE 3 except that its output is nonlinear and it requires additionalcompensation circuitry for the non-linearity output. In this regard, areactance bridge circuit 51b, similar to circuit 46a, would have avariable inductance for one arm and a proper valued resistor associatedwith the variable inductance as another arm. The other half of thebridge comprises the inductor 51a and the resistor 45]).

The roll deflection sensing devices of FIGURES 3 and 4 are describedmore fully in my Patent No. 3,077,800.

FIGURES 5 and 6 show two additional devices for detection of rolldeflection which use changes in reluctance of the magnetic circuit whichbridges one or two small gaps to detect the deflection. As shown inFIGURE 5, two transformers 54 and 55 are located on each side of thesingle small diameter roll 5 and the primary winding of each transformeris connected to a source of A.C. power 47, as provided by an oscillatorsuch as oscillator 75 of FIGURE 9. Transformer 54 has a primary winding56 and a secondary winding 57 and transformer 55 has a primary winding58 and a secondary winding 59. Each transformer is spaced apart from thework roll 5 to form the small gaps 60 and 61 between the roll face andeach transformer and each primary winding directs magnetic flux linkagesto the roll 5 across the gaps and to its secondary winding. It has beenfound that a gap between the roll face and the transformer of about0.005" to about 0.025" effects satisfactory detection of rolldeflection. The two primary windings are connected series aiding and thetwo secondary windings are connected in series bucking.

Connected to the two secondary windings 57 and 59 is an amplifier 50 sothat output voltage of the two secondary coils travels thereto forproduction of a signal.

Because the two secondary windings are connected series bucking, the twooutput voltages in the secondary circuit are opposite in phase and thenet output of the two transformers is the difference between the twooutput voltages.

This net output voltage is related in amount to the magnitude of thedeflection and is directional in accordance with the direction ofdeflect-ion. An amplifier 50 generates from this net output voltage asignal which is related to the amount of deflection and which hascharacteristics of direction of deflection.

FIGURE 6 shows a single transformer 62 positioned on one side of thesingle small diameter work roll 5 for detection of roll deflection. Inusing the single transformer, its voltage output to the amplifier 50when there is no deflection of the roll and the roll is in the givenposition in the roll pass is matched with a standard voltage in theamplifier. When there is roll deflection towards or away from thetransformer, there is a resulting increase or decrease in the voltageoutput of the transformer, thereby causing the amplifier to generate asignal of the same character as the signal produced when using twotransformers.

FIGURE 7 shows another device for detection of roll bar 72 on the otherside of the roll 5 is a second bar 73 parallel thereto and having on itsside opposite the other face of the roll 5 a cushion 74 made from amaterial which does not mark or mar the surface of the roll 5 should itcontact same in deflection. This other bar assists to maintain the roll5 within a given range of deflection so that should there be excessivedeflection, the small roll will not break or fracture.

The roll deflection sensing devices disclosed herein have ability todetect very small amounts of roll reflection suhh as 0.0001 from which asignal is produced for maintenance of the roll substantially at a givenposition in the roll pass. Additionally, these devices are such that useof a flood coolant on the mill does not affect their operation or reducetheir ability to detect small amount of deflection.

Referring to FIGURE 9, the linear variable differential transformer '28has connected thereto an. oscillator 75 which supplies AC. power of highfrequency therefor. The signal output of this linear variabledifferential transformer advances to an. amplifier 29 where it isamplified and forwarded to a phase detector 76. This detector rectifiesthe A.C. roll position signal to provide a DC. voltage related to thedisplacement of the roll from its given position in the roll pass with apolarity indicating the direction of the displacement.

A roll position selector 77a produces an adjustable reference DC.voltage so that a position at which the roll is maintained can beselected by a mill operator. This reference DC. voltage along with theoutput of the phase detector 76 is fed to a difference amplifier 78.which provides an output voltage or error signal related to thedifference between the actual roll position and the desired positionchosen on the selector 77a. The

output voltage signal from the amplifier 78 is related in magnitude tothe amount of deflection and is related to deflection which comprises atube 63 for delivering a fluid such as oil against the face of the roll5 from a source of oil entering the tube through a flexible pipe 64. A

nozzle 65 of the tube is opposite the face of the roll 51 and separatedtherefrom by a film of oil. The pressure of the oil issuing from thenozzle 65 in combination with the pressure of a spring 69a, to bedescribed hereinafter, may be such that the nozzle backs away from theroll 0.0001" to about 0.001. Accordingly, the nozzle rides this film ofoil and avoids a metal-to-metal contact with the roll to eliminatemarking the roll face. The rear end 66 of the tube 63 engages an upperportion 67 of a pivoted arm 68 maintained in its neutral positioncorresponding to zero deflection of the roll from its given position inthe roll pass by a spring actuated plunger 69 in contact with an upperportion of the arm. The lower end 70 of the arm 68 engages one end of arod 71 which carries a magnetic core (not shown) corresponding to core39. This core is disposed in a linear variable differential transformer28a identical to the transformer 28. Consequently, defiection of theroll toward and away fro-m the nozzle 65 operates the linear variabletransformer 28a in the same manner as transformer 28 to detectdeflection of the roll.-

A bar 72 extending substantially parallel to the longitudinal axis ofthe roll 5 carries. the tube 63. Opposite the the direction ofdeflection.

The push-pull output amplifier 15 receives the output DC. voltage signalfrom the difference amplifier 78 and provides sufficient power to drivetwo separate push-pull circuits which deliver portions of the outputvoltage signal of the amplifier 78 to the fast acting regulation system19 (FIGURE 10) and the slow acting regulation system 17. A first portionof the output of this push-pull amplifier '15 is transmitted to oneseparate. push-pull circuit 79' comprising arate generator 80 and. anattenuator 81 connected in parallel with a frequency compensationnetwork 82 and a second attenuator 83. This first portion, like theoutput voltage signal of the amplifier 78, has a magnitude related tothe amount of deflection and is related to the direction of deflection.The rate generator 80 is a differentiating circuit that gives an outputsignal related to the velocity of the deflection.

The frequency compensation network 82 controls the higher frequencyphase of the circuit and amplitude response of feedback circuits to bedescribed hereinafter.

V The attenuators 8'1 and 83 control the gain of a feedback loop and theamount of dam'pening.

The output of this parallel circuitry advances to an adder 84 whichcombines the roll position error signal of the compensation network 82and the rate signal of the rate generator 80 in the proper phases toproduce an output error signal. This sign-a1 is fed to the slowregulation system 17 through the push-pull driver amplifier 16, which isin circuit with two control fields 85 and 86 of a rotating amplifier 87(FIGURE 10), such as Amplidyne, Rototrol, Regulex regulators.

A second portion of the output of the -push-pull amplifier istransmitted to a second separate push-pull circuit 88 identical to thatcircuit 79 comprising the rate generator 80, frequency compensationnetwork 82, the two attenuators 81 and 83 and the adder 84. From thecircuit 88, the resulting output error signal is transmitted to the biasand trigger generator 18 connected to thyra- 11 trons which are a partof the fast acting regulating system 19.

The reference voltage produced by the roll position selector 77 iscarefully regulated so that it does not fluctuate with line voltage,load or temperature changes. This reference voltage is derived from acalibrated roll position setting potentiometer located on the mill andconvenient for the operator to select a given position. This referencevoltage is then used to preselect the performance level required of theregulated quantity which is a current difference corresponding to torquedifferentials in the mill motor armatures.

Maintenance of the small roll in the given position requires thatoverall performance of the regulating system consisting of the fast andslow systems prevent overor undershooting which can bring aboutoscillations of various frequencies in the roll. In this regard, varioustime constants of various elements of the mill, both electrical andmechanical, which add up to an overall time constant, must be taken intoconsideration and each individual time constant reckoned with indesigning the regulating system to prevent oscillation.

It has been found that time constants in the various components of theelectrical system can be varied within reason by changes in L/R ratiosof each circuit. In this connection, the L/R ratio can be shortened byincreasing R through addition of external resistors which, of course,effect power losses and require an increase in size or capacity ofcomponents in the circuits.

The given position referred to in this application includes a small bandof movement such as plus-minus 0.0005, and on wide mills, may be plusminus 0.005. Within this small band of movement, I achieve regulation ofdeflection of the roll so that the deflection does not exceed on eitherside of a given line substantially parallel to the longitudinal axis ofthe rolls, the ranges set forth.

Inorder to achieve very fast and careful regulation of deflection of theroll, it is mandatory that the upper and lower driven mill rolls haveseparate motors to permit effecting a change in apportionment of thetorque applied by the motors to the driven rolls, and preferablyeffecting the change in apportionment of the torque between the two rolldrives without affecting the total amount of torque imparted to therolls themselves. It is further preferable that the change inapportionment be made without affecting the main generators currentoutput. The foregoing roll drive, in combination with my dual regulatingsystem, achieves correction for roll deflection in intervals such as 4to 17 or 20 milliseconds.

Referring to FIGURE 10, a main generator 89, driven by an AC. motor 90,is connected to the mill motors 10, L1, 12 and 13 with mill motors 12and '13 driving the top backing roll 1 and connected in parallel, andmill motors and 11 driving the lower back-ing roll 2 and connected inparallel. Mill motor 10 is in series electrically with mill motor 12, asis mill motor 11 in series electrically with mill motor 13, and motors11 and 12 are connected to one side of the generator 89 and motors 10and 13 are connected to the other side of this generator.

Connected across natural neutral points 91 and 92 on line 93 in the millmotors power circuits is the buckboost generator 20 driven by its AC.motor 94.

The buck-boost generator has a main field 95 connected to the Amplidyneregulator 87 of the slow acting regulation system 17, and a fast field96 is in circuit with the fast acting regulating system 19. The fastfield is a relatively few-turn coil of heavy wire for current input fromtwo back-to-back connected bridge rectifiers 97 and 98 so that theoutput from the bridges is transformed to field flux which adds to orsubtracts from the flux of the main field 95. On the other hand, themain field 95 is a relatively high impedance winding having more turnsper coil of small size wire.

Since the buck-boost generator experiences rapid changes in field flux,its field frame is preferably a laminated construction of good gradeelectrical sheet for fast response and low hysteresis and eddy currentlosses.

Through addition to or subtraction from the field flux of the main fieldand the fast field 96 of the buckboost generator 20 by operation of thefast and slow systems 17 and 19, I produce a steep rise or fall ininduced voltage of the armature 99 of the generator 20 and provide acorresponding steep rise or fall buck-boost output armature current.Accordingly, the armature current of the generator 20 flows in eitherdirection in line 93, as indicated by arrows 100 and 101 (FIGURE 10) andincreases the armature current in the upper roll drive motors indirection 100, while simultaneously decreasing armature current in thelower roll drive motors. This effects a change in the apportionment oftorque delivered by the two roll drives and thereby moves the small workroll towards the given position or maintains same thereat. Of course,flow of the armature current of the booster in the direction of arrows101 has the opposite effect as to increasing armature current in thebottom roll drive and decreasing it in the top roll drive. Thus, thetotal amount of torque imparted to the driven rolls remain substantiallythe same but the amount of torque delivered to one driven roll relativeto the other driven roll is affected whereby correction for deflectionand maintenance of the roll substantially at the given position isachieved.

' Forcing the fields 95 and 96 of the buck-boost generator 20 withhigher than normal field supply voltage from the slow acting regulationsystem 17 and the fast acting regulation system 19 produces a fastresponse from the generator 20. Additionally, an external resistor 102in series with the generator armature 99 reduces the time constant ofthe regulated power circuit, including the mill motors 10, 11, 12 and 13by reducing the L/R ratio. However, use of this resistor is notessential.

Considering the slow acting regulation system 17, the Amplidyneregulator 87 is driven by the AC. motor 94a and has the two matched highimpedance control fields 85 and 86 connected to the driver amplifier 16.One fields connection is reversed as to the other so that when eachreceives an equal amount of DC. output voltage from the amplifier 16,the resultant magnetic field fiux is zero for one cancels the other.

The driver amplifier 16 (FIGURE 9) includes circuits which affect itstime-rate output such as gain, rate feedback, bias and adjustable timeconstants, and additionally, has two output push-pull circuits whichreceive the push-pull signal from the adder 84. When the push-pullsignal is received by the driver amplifier 16, one output voltage israised an amount equal to that that the other output voltage is lowered.Which output circuit has its voltage raised is dependent upon thedirection of deflection of the roll 5, and the amount of raise and ofreductiofii is dependent upon the amount of deflection of the roApplication of this DC. output voltage from the driver amplifier causesone control field 85 or 86 to drive to a higher excitation level, whilethe other control field is driven to a lower excitation level to effecta net ampere turn current in one direction or the other to induce avoltage in the armature of the Amplidyne. Arrows 103 and 104 indicatethe direction of voltage induced in the armature 105 of the Amplidyne 87by control fields 85 and 86. Accordingly, the armature 105 of theAmplidyne delivers a variable and directional excitation current to themain field 95 of the buck-boost generator 20 which current must havereversible polarity to effect maintenance of the roll 5 in the givenposition.

A negative feedback for the armature 105 of the Amplidyne comprises adifferential field 106 connected across the armature 105 and a networkof back-to-back connected zener diodes 107 and 108. This negativefeedback improves transient performance and stability of the Am-

